MIXED CHLORIDE PHOSPHINE COMPLEXES OF DIRHENIUM CORES - 1 - NEW REACTIONS AND UNPRECEDENTED STRUCTURES INVOLVING TRIMETHYLPHOSPHINE

The unusual 1, 2, 7-isomer of Re2Cl5(PMe3)(3) (1) has been used as a s tarting material to prepare previously unknown dirhenium complexes. On e-electron reduction of 1 by cobaltocene followed by nonredox substitu tion of the resulting anionic species with PMe3 led to the formation o f a triply bonded 1, 2, 7, 8-Re2Cl4(PMe3)(4) (2). In the crystal struc ture of 2, phosphine ligands on both metal centers exhibit a cis arran gement with a P-Re-P angle of 93.3 degrees in contrast to the well-kno wn type of 1, 3, 6, 8-isomers with a trans arrangement of the monodent ate phosphines connected to each metal atom. Complex 2 represents the first example of an isomer of this type in the large M2X4(PR3)(4) clas s of compounds (M = Re, Tc, W, Mo; X = Cl, Br, I; PR3 = monodentate ph osphine). The one-electron oxidation product of 1 cocrystallized with one molecule of tetrabutylammonium chloride afforded Re2Cl6(PMe3)(2) ( 3), for which all previous synthetic attempts had failed. This quadrup ly bonded complex exhibits an unusual 3-fold disorder of the Re-2 unit with equal populations for all three orientations. We also report tha t when the ''classic'' reaction of octachlorodirhenate anion, Re2Cl82- , with trimethylphosphine is carried out in benzene at room temperatur e the reduction processes do not occur and the product is a novel para magnetic complex, Re2Cl6(PMe3)(4) (4), which does not have a metal-met al bond (the Re-Re separation is 3.8476(4) Angstrom). Another interest ing feature of compound 4 is that the PMe3 ligands have a cis disposit ion at each rhenium center and are located in the same plane as the me tal atoms and bridging chlorine ligands. For such a ligand arrangement the molecule of 4 is the only example of a nonmetal-metal-bonded dinu clear compound with monodentate phosphine ligands.